This invention relates generally to computed tomographic (CT) imaging methods and apparatus and more particularly to CT methods and apparatus having a plurality of detector arrays.
At least one known CT imaging system utilizes a multi-slice detector array comprising a scintillator and a photodiode arrays. Each detector array contains a plurality of detector cells that are used to measure attenuation information of an object for image back projection for a single or multiple slice planes through the patient. As used herein, a “detector cell” is the smallest portion of a detector array from which attenuation data can be obtained.
At least one known CT imaging system utilizes multi-energy scanning to differentiate tissues or materials having different densities. For example, CT imaging systems have been used to distinguish calcium and iodine in medical applications. One known method uses a single slice image obtained from a CT imaging system having a single detector system. Two different X-ray beam filters are used, or two different x-ray tube peak voltages are used with beams that exactly overlap spatially. The two different filters or tube voltages are applied at different times to obtain two images of the same volume. These two images are processed to separate material of varying densities. For example, in at least one known methods, processing involves image subtraction. A slice of data is be acquired at one x-ray tube peak voltage or using a first filter. Next, the x-ray tube peak voltage is changed or a filter at the x-ray tube is changed, or both, and a second slice of data is acquired at the same location of the imaged object. The two slices of data are be processed to separate materials of varying densities within that slice plane, again usually by image subtraction. However, this process is complex and time consuming, and therefore has not gained wide acceptance among CT users.
In another known CT apparatus, a simpler dual energy or multi-energy detection process is used. However, direct conversion CT detectors, when utilized exclusively in a CT imaging apparatus, cannot count X-rays fast enough to support CT flux rates and scan times. Such detectors used in the current mode have high non-linearities that make it difficult to achieve artifact free scanning.